Depolymerization of ring substituted methyl styrene polymers



y Patented Mar. 231 945 DEPOLYMERIZATION on RING sensuru'rnn METHYL STYRENE roams Frank l. Soday, Swarthmore, 1a., asslgnor to The United Gal Improvement Company, a corporation of Pennsylvania m winz. Application January 20,1942,

SerialNo.427,41'l

I Claims.

This invention pertains generally? to the depol- 'ymerization' of ring substituted methyl styrene polymers. s

More specifically, this invention pertains-to the isolation of one or more ring substituted methyl styrenes in relatively pure form from a fraction or solution containing the same by subiectins' said fraction or solution to polymerization conditions, replacing the unpolymerized material in said fraction or solution with a solvent or mixtureof solvents having a boiling point or points substantially removed from that of the mono-u meric ring substituted methyl styrenes present in the original fraction or solution, followed by depolymerizing the said polymers which may be in v various forms such'as homopolymers of any one i or more of the ring substituted methyl styrenes,

or copolymers of the isomeric ring substituted methyl styrenes, or mixtures thereof, and separating the added solventor solvents from the depolymerized material. a

- Another object of the invention is the recovery of one or more ring substituted methyl styrenes essarily cdntain only one of the individual methyl from the still residues commonly obtained as a by -product oi the fractionation of fractions or mixtures containing one or more ring substituted .methyl styrenes by replacing the. unpolymerized material with a solvent or mixture of solvents u having a boiling point or boiling range different from that of the mono 'ne c ring substituted methyl styrenespresent in the still residue in the form of polymers, depolymerizing the said polymers, and separating the added solvent from the depolymerized material.

A further object of the invention is the depolymerization of polymer or polymers obtained from one or more ring substituted methyl styrenes by the application of heat to a solution of the said polymer or polymers when in the form "of a thin layer or film, the solvent employed in making the said solution having a boiling point ofpoints different from that of-' the monomeric rin'g' substitul methyl styrenes. v p

Another object of the invention is the depolymerization' of the said solution of such polymer or olymers in a solvent having a boiling point inspection of the following specification and I throughout the specification is intended to embrace the presence of one or more ring-substituted methyl styrenes such as ortho methyl styrene, meta methyl styrene, and para methyl styrene, although the presence of side chain substituted styrenes and particularly side chain substituted methyl styrenes is not precluded as will hereinafter appear. v

My present invention involves the step of depolymerizing methyl styrene polymer, which may be present in the form of ,homopolymers of the individual methyl styrenes and/or in the form of copolymers thereof.

The fractions orsolutions constituting one preferred source of my starting material do not'necstyrenes :but in fact may contain substantial quantities of two or more of the individual methyl styrenes in admixture. Consequently, upon polymerization'nisueh fractions or solutions the monomeric components thereof may form not only homopolymer of a single methyl styrene but also a plurality of homopolymers of such individual methyl styrenes as may be present, as well as copolymer or copolymers of the methyl styrenes where two or more are present.

The extent to which one or more homopolymers and/or copolymers of methyl styreneare formed .in any given case may depend upon a number of factors at present'not entirely understood, such as the ratio of monomeric material present in the fraction or solution (or the "ratio; to each other of the several monomeric constituents when morethan one are present), the nature and quan- 'tlty of impurities present, the polymerizing conditions such as temperature, type of catalyst, if

any, etc., and perhaps other factors.

A "homopolymer may be said to be apolymerization product resulting from the combination of molecules of monomer and/or polymers of the same monomeric 'polymerizable compound. I A "copolymer, on the other hand, ma be defined as a' polymerization product resulting from ring substituted methyl-styrenes and/or ring sub- 7 stituted methyl styrene copolymer, in any combination such as may result from the polymerizationof one or more ring substituted methyl styrenes.

In the various processes which have been developed for the manufacture of artificial gas,

- such as oil gas, carburetted water gas, or coal gas, considerable quantities of tar are produced, and the gas contains substantial quantities of J readily condensible materials.

The condensateobtained from the artificial gas, as well as the light oil obtained upon distillation of the tar, constitute sources for many unsaturated and aromatic hydrocarbons. The light oil obtained from the pyrolysis of petroleum or of petroleum hydrocarbons is especially rich in unsaturated hydrocarbons, particularly when "temperatures in excess of 1100" F. have been em-' ployed in the cracking operations.

Among these unsaturated hydrocarbons are the following methyl styrenes,

on=om p-Methyl styrene C H=C Hr m-Methyl styrene and ' CH=CH2 o-Methyl styrene Although the'light oil from which these methyl" 1 for fuel purposes.

This 1ack of commercial utilization of these desirable methyl styrenes can be directly traced to the lack of a satisfactory method for their isolation in a pure or relatively pure" form.

hereinafter set forth, and the 'depolymerization of the polymer is preferably carried out under carefully controlled conditions in order to obtain satisfactory yields of the desired methyl styrenes.

, With respect to the type of solvent to be em-- ployed, I have found that a number of solvents good grade of methyl styrene, in the practice of the process to be more particularly described herein. Thus, for example, the use of halogenresults in the production of monomeric methyl styrenes containing traces, or more, of halogen.

I have found that the presence of traces, or

more, of halogen in monomeric methyl styrene renders it'relatively less desirable for the production of a good grade of polymethyl styrene. Thus, such polymers frequently are yellow in color, their electrical properties are inferior, and they possess relatively poor thermal and mechanical properties. This is due to the inclusion of at least a portion of the halogen present in the finished polymer. However, where such conditions exist, and if desired, I may subject the resulting resins which may be of relatively less desirable quality to a refining treatment for the purpose of removing and/orinactivating undesirable impurities contained therein, thereby producing resins which may be fairly comparable in quality with those resins prepared, from monomeric methyl styrenes having no such undesirable impurities. 0n the other hand the resins contaming traces, more or less, of impurities of the type indicated may be entirely satisfactory for,

As a result of extensive experimentation, I have discovered that pure or substantially pure methyl styrene may be obtained in good yields by the polymerization of fractions or solutions containing one or more methyl styrenes, replacing the unpolymerized material with a solvent or mixture of solvents having a boiling point, or boiling points, substantially different from that of the methyl styrene, or mixture thereof, present, followed by the depolymerization of the said solution, preferably in attenuated form, by the application of heat thereto, and separating the added solvent from the depolymerized material.

While any desired method may be used for the polymerization of the desired fraction or solution, the solvent used to prepare a solution of the methyl styrenepolymer is preferably carefully selected in accordance with the teachings certain purposes where color, and relatively some-' what inferior electrical, thermal and/or mecharrh cal properties are of little or no importance, and consequently such resins may be used without further refining, if desired.

In addition, I have found that certain types of sulfur-containing compounds also are rela-' tively less desirable solvents for methyl styrene polymers prior to the depolymerization thereof. Thus mercaptans, disulfides, and certain other sulfur containing compounds may decompose to some extent during the depolymerizing operations, forming free sulfur and/or sulfur-containing radicals which may subsequently react with the methyl styrene present to give a product containing traces, or'more, of sulfur. I have found that methyl styrenes containing traces, or more, of sulfur or of sulfur compounds frequently produce polymers which are inferior to those bbtained from sulfur-free methyl styrenes, particularly from the standpoint of their electrical properties.

However, as in the case when halogen-contain;- ingsolvents are employed, the resulting resins may, if desired, be further refined to remove and/or inactivate undesired impurities contained therein. Also as in the case whenhalogen-contaming solvents are employed, the resulting resins may be entirely satisfactory for certain uses, and therefore may be employed in such cases without further refining or purification. v

y In addition, theuseof numerous other types of commercial solvents is preferably avoided when depolymerizing methyl styrene polymers due to their tendency to impart undesirable properties to the monomeric methyl styrene obtained subsequently, such as imparting color or colorformirig properties thereto.

The solubility characteristics of the solvents to be employed for this purpose preferably are also carefully investigated. Methyl styrene polymers,

particularly thosehaving a fairly high molecuboiling dead oil produced during the'pyrolytic decomposition of petroleum oil such as during the manufacture of combustible gas with 'pyrolyzlar weight, are relatively, or almost completely,

insoluble in certain on the materials frequently employed as solvents in the field of organic chemistry, such as esters and ethers. It will be obvious to those skilled in the art that'the use of such materials is to be avoided, since they are not solvents as the term is employed herein.

In other words the term solvent," unless otherwise qualified, is employed in the present spect-v fication andclaims in the sense of a material having at least a substantial dissolving power for methyl styrene polymers.

Finally, the solvent used for dissolving the methyl styrene polymers prior to their depolying temperatures above say .ll00 F., said solvent fraction being further characterized in being relatively free from resin-forming unsaturated hydrocarbon components which are previously re-& moved therefrom. 4

.In addition, other hydrocarbon solvents also may be used with excellent results, especially if they contain a substantial proportion of aromatic -'and/or naphthenic hydrocarbons and have no considerable portion boiling between 160 and 180 C. and more especially if they have no considerable portion boiling between 150 and 190 C. Such solvents as the foregoing are especially resistant to chemical action under the conditions merization preferably should be relatively stable during the depolymerizing operation, among other reasons in order that it may be reused in the process, and to prevent contamination of the methyl styrene obtained.

The solvent or solvents are accordingly preferably selected from materials which are inert, or relatively inert, under the conditions obtaininz during the process, and preferably from the time such solvent is first admixed withpolymer and/or substituted for unpolymerized material present 'until the time the solvent is separated from the obtaining throughout the process, and particu-.

larly during the depolymerization reaction.

Solvents boiling both above and below the boiling points, or boiling range, of the methyl styrenes may be used for this purpwe, or mixtures of such solvents may be employed, provided the boiling characteristics of such solvent, or mixtures of solvents. are as indicated above. Somewhat different procedures may be employed in substituting the desired solvent, or 'mixtures' thereof, for the unpolymerized material present in the polymerized light oil methyl styrene fraction depending, among other things, upon the boiling point or range of the solvent ormixture of solvents employed for this purpose.

Thus, when a solventhaving a boiling point or range substantially above that of methyl styrene,

I or. mixtures thereof, is employed the, solvent or ous conditions which obtain during the course of my process. From another point of view, my preferred solvents may be said to be non-interfering" under the conditions obtaining, in that not only do they have no, or at most only a slight;

chemical activity under-the conditions obtaining,

but also they show little or no tendency to inter-. fere subsequently with the ready separation of the desired monomeric products of depolymerization. 5

As a result of extensive experimentation, I have discovered that hydrocarbon solvents are particularly satisfactory foruse in preparingmethyl solved in the desired'solvent, or mixtures thereof.

styrene polymer solutions prior to the depolymerization thereof. In particular, I have found that aromatic-type solvents, such. as benzene, toluene, xylene, and any other aromatic solvent boiling, or substantially all of which boils, below 160 C. or above 180* C. may be used for this purposewith excellent results. Even'niore desirable or substantially all of which boils, below 150 C. or above 190 C. 'Such boiling characteristics may for convenience be defined by stating that mixture of solvents may be added to the polymerized light oil methyl styrene fraction, after which the unpolymerized material originally present may be removed by any desired method such 40 as by distillation, resulting in a solution of methyl styrene polymer in the desired solvent.

In the case of a solvent, or mixture of solvents, having a boiling point, or range, substantially below that of methyl styrene, or mixtures thereof, the-unpolymerized material first is removed from the polymerized materialfsuch as by distillation under reduced pressure with the aidof steam or an inert gas, or by spray drying methods, or otherwise, after which thepolymer is dis- Thus, for example, the polymerized methyl styrene fraction may be hardened .by steam under reduced pressure in a suitable vessel, afterwhich the desired solvent is introduced and the mixture thoroughly agitated until complcte solu-' results may be obtained when the solvent boils,

the solvent or solvents have no considerablef portion boiling between the boiling point limits above set forth. I

-. In the case of the employment of a polymerizable solvent forthe polymer reference is made tion has been attained.

This latter method also can be used to prepare solutions of the methyl styrene polymers insolvents having a boiling point or range above that vof the methyl styrenes, as well as for the preparation of solutions of the said polymers in a mixture of solvents having boiling points both above and below that of the methyl styrenes.

to my copending application, Serial No. 428,832,

filed January 30, 1942.

As an example of a solvent boiling substantially above 180 C. which may be'employed with good results, there may be mentioned a solvent hydrocarbon fraction all, or a preponderant portion, of which boils between approximately 200 C. and approximately 240 0., said solvent fraction being essentially of a highly saturated aromatic nature, and being obtained from'a relatively high .while the methy1 styrene polymer solutions may be depolymerized by any desired method, such as by batch depolymerizing methods, I have found that excellent results may be obtained by the application of heat to solutions of such polymers in attenuated form. I

An excellent source of methyl styrene fractions which may be used as raw materials for As a result ,of extensive experimentation, I have found that light oil fractions derived from oil'gas andboiling within the range of approxi mately 160 to 178 C. contain substantial quantities of. methyl styrenes, Thus, for example, the

predominating unsaturated hydrocarbons present in light oil fractions boiling in the range of 165 to 175 C., and more particularly in the rangeof 167 to 173 0., usually are para styrene and meta methyl styrene.

The concentration and purification of the methyl methyl styrenes contained in such fractions is proximately the same boiling range, it has been found to be practicably impossible to isolate relatively pure methyl styrene from such frac 'tions by fractional distillation methods, even though columns having an efficiency of 100 plates or more have been utilized for this purpose. In addition, such methods have been attended by the loss of relatively large quantities of the methyl styrene in the form of polymers or still residues due to the pronounced tendency of such materials to polymerize under the influence of the elevated temperatures required in such fractional distillation operations. Although the fractions containing larger proportions of both methyl styrenes and the methyl phenylacetylenes. As the latter compounds are very undesirable ingredients in methyl styrene fractions,

particularly when such fractions are to be used for the preparation of resins, in which case the methyl phenylacetylenes act as polymerization inhibitors and deleteriously affect the quality of the resins obtained subsequently, the improvement in the quality of the methyl styrene fractions due to the increase in the concentration of' the methyl styrenes contained therein is more than counterbalanced by the corresponding increase in the concentration of the methyl phenylacetylenes.

The isolation of pure or substantially pure methyl styrene from fractions or solutions containing the same according to the method disclosed herein is free from the foregoing objections, since I have discovered that practically none of the impurities present in such fractions or solutions react in the same manner as the methyl styrene in the polymerizing and subsequent depolymerizing steps. Thus, for example, the polymerization ofa light oil methyl styrene fraction, the substitution of a solvent having a boiling point or points essentially digerent from that of methyl styrenes for the unpolymerized material present, and the depolymerization of the said polymer solution by the methods to be more particularly described herein, results in the isolation of pure or substantially pure methyl styrene quantity of such polymers obtained can be re- 1 duced substantially by the use of certain inlu'bitors such as hydroquinone, by the application of reduced pressures say of the order of 8' of methyl styrene fractions'increases with increasing concentration of such fractions. When a concentration of approximately 80% of methyl styrenes in a given fraction has been achieved by fractional distillation methods, the rate of increase of "concentration of the methyl styrenes in such fractions by further fractionation isalmost exactly counterbalanced by the increased rate of polymerization of the methyl styrenes present. usually leads only to the conversion of larger quantities of the methyl styrenes present to poly. mers without increasing the concentration of such fractions to any substantial extent.

In addition to the foregoing, the use of fractional distillation methods for the concentration of methyl styrene fractions almost invariably results in the similar concentration of certain of the undesirable impuritiespresent in such fractions. Thus, for example, the fractional distillation of light oil fractions containing methyl styrenes invariably results in the isolation of containing very litle, if any, of the methyl phenylacetylenes.

What has been said with respect to the elimination of the methyl phenylacetylenes by the application of the concentrating method described herein applies equally well to practically all of the other undesirable impurities present in fractions or solutions of methyl styrenes in general, such as other substituted acetylenes or phenylacetylenes, as well as oxygen-, nitrogen-, and sulfur-containing impurities.

It is apparent, therefore, that the application of the method described herein to methyl styrene fractions or solutions results in (a) the concentration of the methyl styrene present and (b) the elimination of ayery considerable portion, if not all, of the undesirable impurities present.

Fractions or solutions containing almost any I desired proportion of one or more methyl styrenes boiling point substantially different from that of r the methyl styrenes present substituted for the Consequently, continued fractionation unpolymerized material present, the polymer solution subsequently depolymerized to form methyl styrene, and the solvent and the methyl styrene separated by any desired method, such as by distillation. However, I generally prefer to use fractions containing somewhat larger quantities of methyl styrene, say 10% or more, for practicable reasons. Fractions or solutions containing 20%, or more, of methyl styrene, such as 30% to 80% or'higher, are particularly desirable for this purpose.

The initial step in the isolation of methyl styrene from fractions or solutions containing the same, namely, the polymerization of such fractions orsolutions, may be carried .out in any desired manner.

Thus, for example, such fractions or solutions may be polymerized bythe application of heat.

' trifuging.

be handled somewhat more easily inthe depoly-v merizing processes described herein, due totheir friable nature and the relative ease with which they may be dissolved in certain solvents, a pre ferred embodiment of this invention is the use of such low molecular weight polymers in such processes.

Thus, for example, light oil methyl styrene fractions boiling in the range of 160 to 178 (3. may be polymerized by the application of temperatures in the range of 150 to 200 C., or higher, for periods ranging from one to four days, for

example, to give excellent yields of polymers which have a low molecular weight, are friable, and may be dissolved readily in aromatic solvents.

Airiable polymer may be distinguished from a tough polymer in that "the former cannot be readily molded without fracture whereas the latter can be very readily molded without fracture. In general a friable polymer may also be distinguished from a tough polymer in that it has a relatively low melting point, for example below 150 C. by the "capillary method.

Generally speaking, however. any desired polymerizing schedule may be employed and the polymerization may be carried out at any desired pressure, whether atmospheric or above or below, and in the presence of any desired gaseous substance, such as air, nitrogen, carbon dioxide, and the like.

In addition, catalysts may be used for the polymerization of such fractions or solutions, either alone or in combination with the simultaneous, or otherwise, application of heat. Ex-

amples of such' catalysts are peroxides, such as hydrogen peroxide, benzoyl peroxide, stearyl peroxide, and the like; contact materials, such'as clay, activated clay, carbon, activated carbon, silica gel, alumina, and the like; metallic halides and metallic halide-organic solvent complexes, and especially those which are characterized by readily hydrolyzing in the presence of Water to give an acid reaction, such as aluminum chloride,

boron trifiuoride, aluminum chloride-diethyl ether complex, boron trifluoride-diethyl ether complex, and the like; ansolvo' acids such as borofluoroacetic acid;. mineral acids and mineral acid-organic solvent mixtures or reaction produ'cts, such as sulfuric acid and sulfuric acid-diethyl ether mixture: reactive metals such as sodium; and other catalysts or mixtures thereof.

After polymerization, such catalysts preferably are removed from the polymers prior to their de- 1 polymerization by the methods to be more particularly described herein. In the case of contact materials, such catalysts usually can be removed from the polymer solution by filtration or cen- In the case of metallic halides and complexes thereof, ansolvo acids, and mineral acids, such acid-acting catalysts preferably are hydrolyzed or neutralized by the addition of an alkali or an aqueous solution of an alkali, followed by filtration or centrifuging to remove the hydrolysis products. Reactive metals may be removed by the addition of alcohol, followed by filtration.

Other methods of removing the catalysts employed in such processes may be used, it desired.

By the use 01' catalysts in conJunction with the use of elevated temperatures, polymers possesslng almost any desired physical properties may be obtained. In addition, the complete conversion oi the methyl styrene present in a given fraction or solution may be accomplished in a minimum of time by the use of certain of the catalysts'described in combination with the use of elevated temperatures.

The methyl styrene present in a given fraction or solution may be converted to polymers possessing very low melting points by'the use of certain catalysts in conjunction with the application of elevated temperatures. Thus, the polymerization of a light oil methyl styrene fraction with activated clay at elevated temperatures resulted in the production of'a polymer which was liquid at room temperatures. The use of such low melting or liquid polymers may be desirable in certain of the depolymerizing processes described herein, as will be more fully explained hereinafter. r

By the. use of rigorous polymerizing methods, dimers, trimers, and other relatively low molecular weight products may be obtained from methyl styrene fractions or solutions. In general, it may be said that low molecular weight polymers of this type may be used in the depolymerizing processes of the type described herein.

Irrespective of the method employed in polymerizing the methyl styrene fraction or solution, the next step in the process involves the substitution of a solvent having a boiling range substantially removed from that of the monomeric methyl styrenes for the unpolymerized material present. The type of solvents which preferably are used for this purpose, and the method employed for substituting the desired solvent or solvents, or mixtures thereof, have been discussed point or points sufiiciently different from that of the methyl styrene or styrenes to be obtained from the depoiymerizing process to be readily separable therefrom, and one which is suiiiciently stable to be substantially unaffected by the elevated temperatures employed in the depolymerizing process and which does not impart any undesired properties to the methyl styrenes subsequently obtained, preferably is employed for this purpose. Suitable solvents for this purpose include benzene, toluene, and xylene, as well as other aromatic hydrocarbons, boiling either below 160 C. or above 180 0., or still more preferably, either below 150 C. or above 190 6.; as well as mixtures of one or more relatively low boiling solvents with one or more relatively high boiling solvents, relative that is with respect to the boiling points of the methyl styrenes.

Other methods of isolating the polymer may be used, if desired. Thus, for example, the poly- The polymer solution also may be processed to remove unpolymerized material, among other ways, by spray drying methods such as by spraying the polymer solution. into a heated tower, either alone or in conjunction withthe use of steam or an inert gas to assist in removing the unpolymerized material, by working the material on hot rolls to remove unpolymerized material,

solvent and methyl styrene, together withthe other constituent or constituents of the copolymer and/or mixed polymer. Such mixture may be treated to recover one or more methyl styrenes by any suitable means, if desired, such as by fractional distillation, suitably under reduced pressure, In this way one or more monomeric methyl styrenes ingood yields may be recovered. as well as good yields of the monomeric nonstyrene type compound or compounds which were present in the form of copolymer and/or mixed polymers, especially where the boiling point or points of the latter monomeric compounds differ sufiiciently from that of the solvent to make In addition to the use of polymers prepared directly by the polymerization of fractions or solutions containing methyl-styrene, methyl styrene polymers obtained from other sources also may be depolymeriaed by the process described herein to form monomeric methyl styrene withexcelient results.

A very satisfactory source of such polymers is the still bottoms or residues obtained as a by- .product of the fractionation of solutions or fractions containing methyl styrene. Thus, for ex ample, light oil obtained from oil gas, or from other sources, commonly is fractionated to obtain fractions containing substantial proportions of methyl styrenes, among other unsaturated hydrocarbons. As pointed out previously, such fractionating steps result in the production of considerable quantifies of polymers from the methyl styrenes present in such fractions, particularly when drastic fractionating methods are employed for the production of fractions containing substantial quantities of methyl styrenes. The still residues obtained from such processes are particularly well adapted to the production of methyl styrene by the depolymerizing met ods to be described herein.

As such still residues are commonly drained from the still pot or reboiler, either continuously or discontinuously, before all of the unpclymer-- ized material has been distilled therefrom in order to assist in the removal of the still residues from the unit, such materials preferably are treated to remove all impolymerized material present prior to the depolymerization of the methyl styrene polymers. The methods discussed previ ously for the removal of unpolymerized material from polymerized methyl styrene fractions or solutions may be used for this purpose with excellent results. 1

If desired, the still residues may be subjected to additional treatment, such as by the application of elevated temperatures and/or catalysts, in order to polymerize all methyl styrene present prior to substituting another solvent or solvents of diilferent boiling characteristics for the unpolymerized material present.

In addition to still residues, methyl styrene polymers derived from the polymerization of methyl styrene fractions or solutions under other conditions such as the polymers obtained when such fractions, or solutions are stored, shipped, or otherwise handled or treated, also may be used for the production of methyl styrene according to the methods described herein.

Reference is made to my copending parent application Serial No. 409,680, filed September 5,

When polymerized material other than methyl styrene is present, the depolymerized material obtained usually comprises a mixture of added separation thereof practicable. If desired, such monomeric non-styrene type compound or compounds may be isolated by similar means or otherwise during the same or in a separate oper .ation, depending in part upon the relation between the boiling point or points thereof and the boiling point or'points of the particular solvent or solvents employed.

For the recovery of both styrene and methyl styrene from light oil fractions containing both. reference is made to my eopending applications Serial No. 427,418'filed January 20,-1942, and Serial No. 430,?17 filed February 13, 1942.

The solutions of methyl styrene polymers or resins suitably dissolved in solvents of the type described herein may be introduced into the depoiymerizing units to be described presently in any desired form. As pointed out previously in discussing the polymerizahon of methyl styrene fractions or solutions, the polymers obtained may be in the form oi high, medium or low-melting polymers or even liquid polymers. Low melting polymers are well adapted for use in the depolymerizing processes disclosed herein.

Thus, a mixture of solvent and polymer may be melted by the application of heat. By the use of this method, relatively small quantities of solvent and-moderate temperatures may be employed inthe production of a liquid mixture to be introduced into the depolymerizing unit. This may be advantageous'in certain cases, partic ularly from the standpoint of solvent economy.

However, I generally prefer to use polymer solutions which are liquid at room temperature as such solutions may be handled with less diflieulty than solutions containing less solvent.

The depolymerization of the foregoing solutions of methyl styrene polymers may be carried out in the presence or absence of certain other diluents in the reaction zone, such as steam, other solvents, particularly relatively low boiling solvents such as propane, butane, pentane, petroleum ether, and inert gases, such as nitrogen, carbon dioxide, stack gases, and the like. These diluents may be heated or superheated prior to their introduction into the reaction zone, in which methyl styrene within a reasonable period of time.

I have found that the use of temperatures above 400 C. and,'particular1y, above 500 C. are very satisfactory for the production of methyl styrene for example, the polymer solution may be pumped into the reaction zone, or it may be forced into the reaction zone by the application of pressure, or it may be drawn into the reaction zone by reducing the pressure therein, or otherwise. The container, pipe, tubes, valves, pumps, and other devices and 'solutions at any given time. Any suitable proequipment used to store the polymer solution prior to its delivery to the reaction zone, and to deliver it to the reaction zone at the desired rate, may be heated by any desired method to insure that the polymer is maintained at the desired temperature, if desired. This maybe accomplished, among other ways, by providing such items of equipment with suitable jackets or coils through which steam or any other desired heating medium may be passed, or by the use of electrical resistance heaters for this purpose, or otherwise.

The polymer solution may be heated to any desired temperature prior to its introduction into the reaction'zone, if desired. Thus, for example, it may be heated to an incipient decomposition temperature, or almost to this point, before being introduced into the reaction zone. In case a relatively low boiling solvent is present. the polymer-solvent mixture may be heated under a pressure sufficient to maintain the solvent in the liquid state at the chosen temperature prior to its introduction into the reaction zone.

An alternative method of introducing the polymer solution to the reaction zone comprises carbureting it with steam, a solvent or other liquid in the vapor state, an inert gas, or other suitable agent. This method is especially applicable to solutions of relatively low-melting polymers possessing an appreciable vapor pressure at temperatures below their initial depolymerizing temperature. Thus, for example, a solution of a liquid methyl styrene polymer may be heated to a temperature of, say, 200 C. in a suitable vessel. A suitable carbureting medium such as, for

example, superheated steam is passed through the heated liquid polymer solution, the mixture of steam and carburetted polymer solution then' be employed for this purpose and/or the solvent present in the carburettor replenished from time to time. A relatively low melting type of polymer also is preferably employed. Gtherwise, the solvent may be removed completely from the carburettor before all of the methyl styrene polymer has been charged to the unit.

In the foregoing methods, the polymer solution may be delivered to the reaction zone in the form of a thin layer or stream, or in the form of a spray or mist of finely divided particles, de pending, among other things, upon the type of fitting employed at the termination of the delivery pipe or other device in the reaction zone.

As pointed out previously, I have found that solutions of methyl styrene polymers may be readily depolymerized to give good yields of the corresponding monomers by the application of heat to only a limited quantity of such polymer Val cedure capable of meeting these conditions may be used for the depolymerization of solutions of methyl styrene polymers.

Thus, for example, the polymer solution may be introduced into a heated vessel provided with a stirring device conforming to the interior thereof and sufliciently close to the sides of the vessel to prevent any undue accum lation of ma-- terial thereon. In general, vessels of this type provided with a stirrer or scraping device extending over the major portion of the interior surface of such vessels, particularly the lower portion thereof in the case of vertical vessels, are well adapted to the production of methyl styrene in good yields from solutions of its polymers by thermal depolymerization. In general, the clearance between the heated walls of such vessels and the agitator or scraper should preferably be less than 4" and, more preferably, less than V the clearance between thetwo surfaces is 1 1;" or less. and optimum results may be obtained when the agitator or scraper actually scrapes the interior surface of the reaction vessel. Thus, for example, vessels of the type commonly employed in the petroleum industry for blending or cornpounding greases, and in which the agitator scrapes the rounded bottom and the lower portions of the sides of the reaction vessel, are well adapted to the preparation of methyl styrene by the thermal depolymerization of solutions thereof. The resin solution is distributed on the bottomand sides of the reactor by means of the agitator blade, the rate of flow of the resin solution and the depolymerizing temperature usually being so regulated that only a thin film of resin is present on the bottom and sides of the reaction vessel at any given period of time. I

The foregoing represents one method of depolymerizing methyl styrene polymer solutions by depositing such solutions in the form of a thin him, or otherwise, upon the interior of a-reaction vessel, an agitator being employed to prevent or retard any undesirable accumulation of polymerupon the interior surface thereof. A large number of similar devices or units embodying the same principles may be employed for the depolymerization of methyl styrene polymer solutions if desired.

t will be understood, of course, that the foregoing units only serve to illustrate one method of realizing the advantages of the invention and are not to be construed as limiting it in any way. In general, any method of depositing a relatively thin layer of the desired polymer solution upon a suitably heated surface will serve to depolymerize the polymer in a satisfactory manner.

Another suitable method for the depolymerization of methyl styrene polymer solutions comprises contacting such polymer solutions with a molten metal, alloy, salt, mixture of salts, or other liquids capable of withstanding relatively high temperatures without appreciable decomposition. During the operation, the molten metal or other material may he agitated if desired.

An excellent method fo' the depolymerization of methyl styrene polymer solutions comprises the application of heat thereto while in a very Excellent results are obtained when ticles. Other methods of accomplishing this purpose may, of course, be used if desired. Thus, for example, the polymer solution may be pumped, flowed, or otherwise delivered to the top of a suitable tower or Vessel and permitted to flow over a perforated plate or screen, or both, or otherwise, in such manner as to disperse the material in the form of very thin streams, or drops, or

otherwise. v

Other methods and devices suitable for contacting the finely divided polymer solution may, of course, be employed. Thus, for example, the reaction vessel or tower may be conical in shape in order to prevent or retard any undue accumulation of polymer on the sides of the vessel. Other refinements will, of. course, be apparent to those skilled in the art.

Another suitable method of depolymerizing methyl styrene polymer solutions is to pump. blow or otherwise force such solutions through The depolymerized materials also may be shockcooled if desired, such as by injecting a spray or stream of water or other cooling medium directly into the depolymerized products obtained from the reaction zone, or by passing the depolymerized vapors through a wash box filled with water, or.

' the shortest possible period of time. Any undue a tubular unit possessing a fairly narrow crosssectional area, preferably while the polymer solution is in 'a finely divided or vaporized form, or otherwise. A pipe coil, tube bundle, or conventional cracking furnace may be used for this purpose with excellent results.

The polymer solution may be charged to a single coil furnace, either alone or in admixture or in combination with steam, another solvent, a gas, or a mixture thereof, the preheating and depolymerizing processes being carried out in the same coil. An alternative method comprises pre-.

heating the polymer solution, or admixture, in one coil, then delivering such preheated material to a second coil in which the depolymerization is affected either alone or in the presence of steam, another solvent, or a gas, or a mixture thereof, which mixture may be added to the polymer solution at the inlet, or within, the second coil. Another method comprises heating the assisting agent, such as steam, another solvent, a gas, or a mixture thereof, in one coil, then delivering such heated assisting agent or agents to the second coil in conjunction with a stream of polymer solution, or a mixture of the polymer solution and steam, another solvent, and/or a gas.

Other methods familiar to those engaged in the pyrolysis of petroleum may be used if desired. Other types of furnaces also may be employed, such as the De Florez furnace, a tube coil immersed 'in a molten metal bath, and the like. In addition, the polymer solution or admixture may be charged to a conventional gas set, or a modification thereof, such as those employed for the production of blue gas, oil gas, carburetted water gas, and the like.

Other methods based upon heating a stream of finely divided methyl styrene polymer solution, either alone or in conjunction with one or more assisting agents such as steam, another solvent, a gas, or a mixture thereof may be used, if desired.

It is to be understood, also, that any combination of the foregoing depolymerizing methods may be used for the production of methyl styrene.

The method of condensing and cooling the depolymerized materials obtained also is important from the standpoint of obtaining good yields. The vapors should be condensed and cooled as rapidly as possible in order to prevent any recombination and to prevent side reactions from occurring to any substantial degree. This maybe accomplished .by conducting the vapors into an efllcient condenser and cooling as quickly aspossible, a satisfactory condenser for this purpose being a water cooled shell and tube condenser.

' increase in the depolymerizing time, or the time required to condense and cool the solvent and depolymerized materials, usually is reflected in decreased yields and in the presence of substantial quantities of higher boiling oils and other undesirable by-products in the methyl styrene obtained.

The steam, solvents, gases, or mixtures thereof, which may be charged to the depolymerizing unit with the polymer solution assist in the re action in many ways. They may serve to transmit heat directly to the polymer solution, to assist in sweeping out the products of the depolymerization from the reaction zone in the shortest possible period of time, and to serve as diluting agents, thus preventing, or reducing the rate of, the recombination of the depolymerized materials. I

By the use of the foregoing methods for the depolymerization of methyl styrene polymer solutions, all .of which are based upon the principle of exposing a limited quantity of a solution of the said polymer in a solvent having a boiling point substantially different from that of methyl styrene to elevated temperatures for a limited period of time under conditions designed to effeet a rapid transfer of heat from the heating surface or medium to the polymer solution and removing the solvent and depolymerized materials from theheating zone and condensing and cooling them as rapidly as possible, excellent yields may be obtained.

The depolymerization is preferably carried out in a relatively short period of time. The application of elevated temperatures to methyl styrene polymer solutions for prolonged periods of time. such as may be encountered for example in batch depolymerizing methods, may result in conversion of a relatively large proportion of such polymers into high boiling oils and similar undesirable impurities. In general, it may besaid that the time of depolymerization is a function of the depolymerizing temperature employed. By the use of the proper type and size of unit, the contact time in the depolymerizin zone preferably r'arelylexceeds 10 minutes and, in most cases will notexceed 5 minutes. Contact times substantially under 5 minutes and, more particularly, under 1 minute, will be found to give excellent results.

By depolymerizing methyl styrene polymer solutions, or mixtures of such methyl styrene polymer solutions with other materials according to the method described, particularly when units of the type illustrated are used for this purpose, excellent yields of methyl styrene monomer may be obtained. Higher boiling oils and/or other undesirable by-products obtained during the depolymerization are readily separable therefrom by distillation in view of their widely different boiling points. Thus, for example. the devolvmerization of methyl styrene polymersobtained from a light oil fraction boiling in the range of 165 to 175 C, will give yields up to 75% by weight of theoriginal polymer, or even higher,

when such polymers are depolymerized according to my invention.

separation of the solvent, or mixture of solvents, and the vhigher boiling by-products from the monomeric methyl styrene, or mixture thereof.

A suitable method for separating monomeric methyl styrene andthe solvent or solvents, and

other materials, present in the depolymerized' product, particularly, when the solvent or solvents employed are relatively inert, comprises the fractional distillation of such material. As

'. After depolymerizing the solution of methyl styrene polymer, the next step comprises the' methyl styrenes are readily polymerized. bythe may be polymerized by the application of heat,

erating temperature. After the solvent has been.

substantially completely removed, the methyl styrene may be distilled at a relatively low reflux ratio, or without the use of any reflux, to separate it from higher boiling by-products.

When a relatively high boiling solvent has been employed in the process, a. fairly high reflux ratio is preferably employed during the distillation of the methyl styrene in order to separate it from the higher boiling solvent and higher boiling by-products present. Under these conditions, a significant quantity of methyl styrene may be converted to polymer.

On the other hand, the use in the processof by desired method, such by fractionation under reducedpressure, or otherwise.

- -It is to be understood that higher boiling oils obtained in the process may be separated from the methyl styrene obtained therein prior to the use thereof by any desired in'ethod such ;as for example by fractional-distillation: under reduced pressure.

Bythe practice of my process, methyl styrene of 98% purity'and higher, is readily obtainable.

For the purposes of the specification and the claims the term-attenuated form" or its equivalent, unless otherwise modified, is intended to embrace sheet form, spray form, discrete particleform, small streamforrn, filament form, vapor form and similarly subdivided forms adapted. for

rapid heat transfer. throughout the body of the 7 material in process. For the 'purpose of the specification and the claims, the term "methyl styrene fraction" is in-[ tended to include various partially polymerized forms thereof, such as the still residues obtained upon the distillation of such fractions.

solvents having a boiling point or points above polymers prior to the depolymerization thereof.

As previously indicated, solvents preferably employed are those capable of remaining passive under the thermal and other conditions obtaining,

'and which therefore not only pass through the process substantially unchanged but which also may be readily removed or separated from, the

reaction products.

As pointed out previously, light oil methyl styrene fractions may contain p-methyi styrene, m-metl'iyl styrene, and/or o-methyl styrene. Upon depolymerization of asolution of the polymer obtained from such fractions, the methyl styrenes obtained may be used'as such, or they While specific procedures for the depolyineri-b zationof methyl styrene polymers in the-form of solutions in solvents having boiling points substantially diiferent from those of the methyl styrenes' have been'particularly described, as well as the units in which such depolymerization may be conducted, it is to be understood that these are by way of illustration- Therefore, changes, omissions, additions, substitutions, and/or modiflcations may be made within the scope of the claims without departing from the spirit of the invention. v

I claim: i

l. A process for purifying ring substituted methyl styrene contained in alight oil ring substituted methyl styrene fraction contaminated with methyl phenyl'acetylene which comprises. polymerizing said fraction, replacing unpolym'erized material present with a relatively inert solvent for the polymer. having no considerable portion boiling between c. and 0., heatin the polymer and said solvent-in attenuated form under temperature conditions at least as high as 350 C. for a period of time suflicientto effect acetylene.

2. A method for purifying rins substituted methyl styrene contained in a light oil rins substituted methyl styrene fraction contaminated with methyl phenyl acetylene which comprises polymerizing said fraction by the application of heat to produce a mixture ofunpolymerized material and polymer of ring substituted methyl styrene, repiacingsaid unpolymerized material with a relatively inert solvent for said polymer having no considerable portion boilingbetween 160 C. and 180 C. and dissolving said polymer therein, heating the resulting solution in attene uated form under temperature conditions at least as high as 400 C. for a period of'time sufllcient to effect depolymerization but not exceeding five minutes. and recovering monomeric ring substituted methyl styrene-in purified form and substantially less contaminated with methyl phenyl acetylene.

3. A method for purifying ring substituted methyl styrene contained in a light oil ring sub-" may be separated, either partially or comp tely. 75 muted methyl m fraction boiling between with methyl phenyl toeilect depolymerization while removing and mo c and 17a '0 and contaminated, with methyl phenyi' acetylene which comprises poly- 'merizing. said fraction to obtain a mixture com-' prising polymer of ring substituted methyl styrene and unpolymerized material, replacing said 'unpolymerized material with a relatively inert solvent for said polymer having no considerable portion boiling between 160 C. and 180 0., heating the resulting solution in attenuated form under temperature conditions between 850 C. and 600 .C'. for a period 01' time suiiicient condensing resulting vapor phase-material substantially as rapidly as formed; and subjecting the depolymerized material and solvent to tractional distillation at subatmospheric pressure and in the presence 01' a polymerization inhibitor to recover monomeric ring substituted methyl styrene in puriiiediorm and substantially less contaminated with methyl phenyl acetylene.

' FRANK J. SODAY. 

